Diols and polyols derived from polymerized fatty acids, i.e., dimerized and oligomerized fatty acids have been suggested.
Processes for obtaining such diols and polyols have been suggested whereby the lower alkyl esters of the fatty acids have been dimerized followed by hydrogenating under relatively high pressure or by dimerizing the fatty acid and then converting the dimerized fatty acid to the lower alkyl ester and then hydrogenating under relatively high pressure.
In view of the fact that use of the lower alkyl ester was a relatively uneconomical pressure in view of the additional costs involved with the esterification stage and subsequent removal of alcohol, direct hydrogenation of dimerized fatty acids that contain free carboxyl groups has been attempted. However, dimerized fatty acids that contain two free carboxyl groups are difficult to hydrogenate.
For instance, the catalysts employed were relatively sensitive to the free acids and to the water of reaction that occurs during the hydrogenation of the acids. Moreover, the presence of the free carboxylic acids has a tendency to attack the equipment, particularly under conditions whereby high pressures and high temperatures are required. This, in turn, has led to use of equipment that requires special corrosion-resistant materials.
In view of the various problems encountered, a high-pressure process whereby the polymerized fatty acid starting material is continually introduced into the reaction medium, i.e., a suspension in an amount that during the hydrogenation the amount of polymerized fatty acid present does not exceed the weight of the desired product present as discussed in British Pat. No. 1,132,033.
Although such process overcomes a number of the concerns and problems previously encountered, such process still requires relatively severe pressures and temperatures that it is necessary to employ high pressure equipment. Furthermore, the process suggested therein requires careful monitoring so that the added acid is maintained within the required limits.